Active studies have been carried out in recent year regarding the commercialization of organic EL devices. An organic EL device enables a high current density with a low applied voltage to achieve the realization of high light emitting luminance and high light emission efficiency. Therefore, commercialization of a multiple-color light emission organic EL display has particularly been anticipated which can provide a highly precise multiple-color or full-color display.
One example of a method of providing a multiple-colored or full colored organic EL display is the “color filter method”, wherein a plurality of kinds of color filter layers transmitting light in wavelength regions specific to the respective kinds are employed. When applying the color filter method, the organic EL device to be used is required to emit light with multiple colors for so-called “white light” including well balanced primary colors (red (R), green (G) and blue (B)).
Various methods have been examined to obtain a multiple color light emission EL device such as: (1) a method of using a light emitting layer including a plurality of light emitting materials for simultaneously exciting a plurality of the light emitting materials, (2) a method of using a light emitting layer including host light emitting material and guest light emitting materials for exciting the host light emitting material to emit light and simultaneously causing energy transfer to the energy levels of the guest materials for resulting light emission, (3) a method of using a plurality of light emitting layers each including a different light emitting material for exciting the light emitting material in each layer, and (4) a method of using a light emitting layer, including light emitting materials, and a carrier transporting layer, adjacent to the light emitting layer and including light emitting dopants, for producing excitons by carrier recombination in the light emitting layer to transfer part of excitation energy to the light emitting dopants from the produced excitons.
In the above-explained multiple color light emission organic EL device, however, the light emission relies on either simultaneous excitation of a plurality kinds of light emitting materials or energy transfer among a plurality kinds of light emitting materials. It has been reported that in such a device the balance in light emitting intensity among light emitting materials varies, which causes possible changes in hues that are obtained.
As a method for obtaining a multiple color light emission organic EL device, a color conversion method has been proposed which uses an organic EL device emitting monochromatic light and a color conversion layer also referred to as a fluorescence conversion layer, a phosphor thin film or a fluorescent material film (see, for example, JP-A-2002-075643 corresponding to US Patent Application Publication No.: US2001/0043043 A1 (film deposition with the use of a metal mask), JP-A-2003-217859 corresponding to U.S. Pat. No. 6,781,304 B2, and JP-A-2000-230172). The color conversion layer being used is a layer including one or a plurality of kinds of color conversion material absorbing light with a short wavelength to convert the light to light with a long wavelength.
As a method of forming a color conversion layer, a method has been studied which is like that of depositing color conversion material by a dry process such as evaporation or sputtering to obtain a thickness equal to or less than 2000 nm, preferably on the order of from 300 nm to 600 nm (see, for example, JP-A-2002-075643 corresponding to US Patent Application Publication No.: US2001/0043043 A1). When forming a color conversion layer by evaporation, a film formed on the whole surface of a display surface makes it impossible to emit light which is resolved into each of the primary colors. Therefore, it becomes necessary to separately form fine patterns each corresponding to a specified pixel by a method of some kind. At present, as a method of separately patterning a thin film of deposited material, a patterned deposition method using a metal mask has been employed. However, although the method of forming a deposition pattern using a metal mask has long been known, in preparing finer mask patterns, limitation in the material and the thickness of the mask limits the level of definition of the mask pattern to 150 to 200 pixels per inch (ppi). Attempting to provide pattern with a definition higher than 150 to 200 ppi, results in problems of increasing complexity, makes it impossible to obtain a higher definition pattern for a large area, and also results in a reduction in yield. For example, the thickness required for a metal mask is around 50 microns in order to provide sufficient strength, but this thickness limits the size of potential openings in the metal mask pattern. Further, differences in the thermal expansion coefficients between the metal mask and the substrate cause alignment problems. Large size metal masks (for example on the order of 730 mm×920 mm) may be misaligned up to several tens of microns due to flexing and expansion problems.
In the case of patterning an organic film, application of a nano imprint technique has been proposed and studied. For example, there is a proposal for applying resist material on a hard substrate and pressing an original form having a specified pattern with protrusions and hollows onto the resist to form electrode separation walls (see, for example, JP-A-2005-158584). Patterning can be provided because of the use of a resist material that has a high fluidity. However, for a color conversion layer formed by deposition or formed only of dyes, it would be difficult to form a desired pattern because of lack of fluidity and a small thickness, on the submicron order, of the color conversion layer.
In view of the above, it would be desirable to provide a patterning method that can be carried out, without using a metal mask, to form a color conversion layer with a fine pattern while avoiding high definition problems and, additionally, to provide a method of manufacturing an organic EL display panel of a color conversion system that emits light with multiple color by using a color conversion layer having the fine pattern.